This invention relates to therapeutic ultrasonic devices and more particularly, but not by way of limitation, to ultrasonic applicators which use a piezoelectric crystal to convert electrical energy into ultrasonic energy.
Ultrasonic transducers which use a piezoelectric transducer in medical imaging and diagnostic applications are known. For example, U.S. Pat. No. 4,870,972 (Maerfeld et el.) discloses a multiple-frequency acoustic transducer for medical imaging. The Maerfeld transducer uses strips on opposite faces of a single transducer to enable each face of the transducer to be used to provide imaging at a different frequency.
U.S. Pat. No. 4,972,839 (Angelsen) discloses an ultrasonic probe for use in medical imaging which has transducers mounted on opposite sides of an acoustically isolating material. The transducers emit different ultrasonic frequencies with one of the transducers selected at any particular time and connected to an associated ultrasonic scanner.
U.S. Pat. No. 4,530,362 (Hetz) discloses an ultrasound transmitting/receiving system for sector scanning which is primarily intended for cardiac examinations. Hetz uses a single electromagnetic drive to activate transducers on opposed ends of an applicator housing. The single drive is used to nullify mechanical inertia forces which would otherwise result within the opposed ends.
U.S. Pat. No. 4,748,985 (Nagasaki) discloses two transducer elements fixed back to back with a damper medium interposed between the transducer elements for use in an endoscope for ultrasonic imaging. The transducers transmit ultrasonic waves, receive the echo and convert the echo into echo signals.
The previously discussed patents do not disclose or suggest a therapeutic ultrasonic device having a single ultrasonic applicator which may be used to apply ultrasonic therapy at multiple frequencies. Therapeutic ultrasonic applicators are used to apply ultrasonic energy directly to the body of a patient, particularly to muscle, fat, or bone, in order to stimulate healing of damaged tissue.
Prior therapeutic ultrasonic devices use applicators having only one applicator surface or diaphragm. Typically, such devices are operable at at least two ultrasonic frequencies and either use two applicators having separate cables, handles, etc., to interchangeably connect the applicators to a control console; or have multiple applicators, housings, cables, etc. connected directly to the control console. The sonic transducer described in U.S. Pat. No. 4,823,042 (Coffey et al.), which is assigned to the assignee of the present invention, and which is incorporated herein by reference thereto, is typical of such devices.
There are problems created by the unavailability of a therapeutic ultrasonic device having a single ultrasonic applicator which will operate at multiple ultrasonic frequencies. For example, the use of multiple independent applicators connected to one control console creates an expensive redundancy of componentry, a higher probability of failure of one of the applicators, and requires the therapist to stop therapy to change the size or frequency of the applicator. If the applicators must be physically changed, i. e., if there is only one connection to the control console and multiple applicators which may be connected thereto, the disconnectable connection creates a point of entry for moisture and other contaminants, the likelihood of a faulty connection, and a likelihood that the control console will not be properly tuned (set to the proper excitation frequency) for the applicator connected to the console, which impairs the therapeutic effects of the applicator. The oscillator or other periodic energy source must be set at a frequency which matches the resonant frequency of the piezoelectric transducer for the applicator to function properly.
Therefore, there is a need for a therapeutic ultrasonic device having a single ultrasonic applicator which will operate at multiple ultrasonic frequencies.